1. Field of the Invention
This invention relates to a magnetic toner used in recording processes making use of electrophotography, electrostatic recording, electrostatic printing or toner jet recording.
2. Description of the Related Art
In magnetic one-component developers, i.e., magnetic toners, used in jumping development, which is one of dry-process developing methods, proposals are made which are concerned with toners made to have a higher circularity in some ways (Japanese Patent Applications Laid-open No. H10-97095, No. 2000-029239 and No. 2001-235897). In the magnetic toners, making them have a higher circularity may be effective in making image quality higher and improving transfer efficiency on the one hand, but on the other hand may bring about difficulties stated below, in some electrophotographic performances. For one thing, the toner tends to faster come into closest packing, and hence magnetic toner particles may so highly rub together or rub against one another as to tend to cause problems of what is called toner deterioration, such that any treating agent added later externally to magnetic toner base particles may become buried in or liberated from toner particles and that the magnetic toner base particles may come to chip. With progress of such toner deterioration, the toner tends to change greatly in charge quantity, or cause image defects accompanied by the faulty charging that may come when any fine powder thereby produced sticks to a toner carrying member or to a toner control member.
To solve such problems, it is attempted to make an improvement by controlling the fluidity of the magnetic toner. For example, available are a magnetic toner in which the degree of agglomeration has been controlled (Japanese Patent Application Laid-open No. 2003-043738) and a magnetic toner the compressibility of which has been controlled (Japanese Patent Application Laid-open No. 2001-35.6516). Taking account of, e.g., adaptation to high-speed machines, however, there still remain problems on improvement in image quality and improvement in durability (running performance).
In addition, as a difficulty caused when the magnetic toner is made to have a higher circularity, a trouble tends to come about in a cleaning step in the electrophotographic process.
As a cleaning means, a blade cleaning means which is so set up that a cleaning blade made of a rubber elastic material is brought into pressure contact with the surface of a photosensitive member is commonly used because of its simple and compact construction and also its advantage in view of cost. This blade cleaning means has a superior cost performance on the one hand, but on the other hand tends to cause melt adhesion of toner to the photosensitive member because it is so set up that the cleaning blade is strongly brought into pressure contact with the photosensitive member surface. Further, it tends to cause faulty cleaning which is a phenomenon that the toner slips away through any slight gap(s) between the cleaning blade and the photosensitive member surface. Such problems may remarkably arise especially when the magnetic toner made to have a higher circularity is used.
With an aim to remedy these, it is proposed that the magnetic toner is incorporated therein with an inorganic fine powder as an abrasive or a lubricant. For example, it is disclosed to incorporate a conductive zinc oxide and tin oxide, or to incorporate cerium fluoride or fluorine-containing cerium oxide particles. (Japanese Patent Applications Laid-open No. S59-168460, S59-170847, No. H01-204068 and No. H08-082949). In these methods, however, such abrasive particles are non-uniform in their hardness and hence they may non-uniformly abrade the photosensitive member surface. Thus, because of a difference in coefficient of friction between the photosensitive member and the cleaning blade at abraded areas and unabraded areas, there have been tendencies that the blade tends to turn up and toner particles tend to slip away. Further, where the abrasive particles have large particle diameters and also have a broad particle size distribution, the abrasive particles must be added to the toner in a large quantity in order to abrade the photosensitive member surface uniformly. However, their addition in a large quantity tends to cause problems on developing performances (in particular, toner scatter, reversal fog, and accumulation of abrasive particles) Such difficulties have also been a matter of importance.